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Posted: 10/3/2005 8:59:47 PM EDT
| Joe called and my Compak 16 will soon be ready. Woweeeee!!!!! |
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Did they quicken the twist, because when I talked to him several months ago he said that in order to shoot 55 grain stuff, he wouldn't go any quicker than 1 in 9", and at that time both recon Rifles and Compak-16s were all 1 in 9". On a semi-related note, Mil/Police gun rag has article this month on Arms Tech's can. 32 dB reduction, quick on and off. Not threaded, but uses a circlip to engage a slot in the FH, then a theraded collar goes over that to keep it secure. |
Joe said their testing with 1 in 7" and 55 grain resulted in some bullets either fragmenting or tumbling in flight. Didn't discuss 1 in 8", but he said he had to go to 1 in 9" to get proper stabilization. This defies conventional wisdom, but perhaps there's something with the gain twist rifling that brings these problems on. Joe's also convinced that in future ops, we might be paired with an ally who uses 55 grain ball as their std round, so he thinks there's good reason to ensure compatibility with this bullet weight given the possibility we might run out of ammo and have to borrow from our friends. In his mind, this is more of a necessity than picking a twist that works with Mk 262 heavy weight bullets. I pressed him on this and he said there's also a added cost factor of redesigning the GT to go to finish up with a quicker twist -- apparently a lot of work goes into programming the rifling machines. Cost may be one thing, but the "55 grain compatability being higher priority than Mk 262 compatibility" argument just didn't pass the common sense test to me, but it's his rifle, his company. Having said all that, I do think his gas trap design is pretty cool, I'd love to try one out some day and see how smothly and cleanly they run. Also, even if his barrels don't give a big velocity kick, they're still supposed to provide high accuracy over a much longer life than CL chrome moly. Even if AT designs aren't revolutionary, it's still good to see small companies trying innovative approaches. I truly wish Joe success. |
The 1/7 and 55gr stuff sounds like bullshit to me. Especially if he's talking about NATO ammo, everyone here who has a 1/7 barrel has never had any issues shooting XM193. Looks like the bullshit that they printed in some gun rag not too long ago. I don't know what the hell kind of 55gr ammo they were testing that "resulted in some bullets either fragmenting or tumbling in flight" but sure as hell wasn't XM193 or any other NATO pressure 55 gr...  JMHO, but I wouldn't spend a dime with a company that makes such obvious B.S. claims. |
I would agree entirely if the barrels in question were conventionally rifled, but his are gain twist. That introduces a new variable into the equation. I have no idea if there's a problem with land engraving tripping over an adjacent land perhaps to the point where bullets get distorted prior to reaching the muzzle. You could be right, it could be pure BS but there could also be something else going on that's unique to his rifling method. |
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Since gain twist starts out slow and gets faster, I would think that twist that varies from 1:20 to 1:7 would be no worse than a fixed 1:7. If they were not so flakey on other facts, I would assume they are correct. But so many things they say don't jive. I am all for polygonal hammer-forged barrels. Gain twist does not seem to offer any benefit in reality -- but it might work from a product-distinction/marketing point of view. I have had some really smart people tell me it was the gain-part of it that allowed higher velocity because it had less startup resistance. If you know about internal ballistics, more startup resistance would give *more* velocity, not less. Adding moly, for example, reduces startup pressure and lowers velocity. That is why molycoating a bullet results in less velocity (if you keep the powder charge constant). I know a few people will write that molycoating increases velocity. That is only if you readjust the powder charge back up to a desired chamber pressure. |
I'm pretty sure the rifling starts off with zero twist, i.e., it's cut straight down the bore. Not sure how far down the twist starts, if an inch or two, or if the twist doesn't kick in until the last couple of inches near the muzzle. Just curious, what are the specific claims they make and which ones don't jive? |
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That because of their proprietary gain/polygonal twist, their 9.5 inch barrel makes as much velocity as a 14.5 inch M4. Chris Bell and others have tested it and it was no faster than other 9.5 to 10.5 inch rifles. I expect a few fps from polygonal twist -- so it should match an HK-53. But you cannot get a 'free' 5 inches. When I emailed Armstech to ask, he repeated the velocity claims that he tells everyone about, but said "I was not personally present when they were last done." So he would not personally stand by the numbers as matching any factory testing, but yet continued to repeat them. David Tubb has tested and ruled out gain twist for competition. He would benefit from more velocity or accuracy if it was possible. I also asked Rock McMillan about gain twist, and he said they tried all that in such and such a decade and there was nothing to it. |
I'm familiar with cbell's data but IIRC he wasn't sure if the model he tested featured GT. Armtech has gone through an evolution of sorts and earliest models were conventionally rifled. Somewhere along the way they converted over to GT and poly, again not sure if those features came in together or if the transition went to poly and then to GT/poly. Mach6 has reported decent velocities, certainly on par if not slightly better than conventionally rifled barrels. I'll agree that he didn't report anything revolutionary, like the "free 5 inches" you mentioned, but it certainly was the equal if not better than other offerings. Even if the claims are bogus, there's certainly no penalty for using this type of barrel. Other AT claims: The gas trap make the rifle run smoother. Cyclic rate is reduced to around 650-700 rpm, using std buffers. A side benefit is port pressure is reduced and gas pressure through the tube is reduced because of the extra gas trap volume. To achieve the same cyclic rate reductions in a more conventional carbine, you need to go MGI RRB, Enidine buffer, heavy springs or carriers. I don't think a 9mm or H3 will give the same result, but even if it does, port pressures and pressure on the keys remain higher. Barrel life is significantly improved -- special SS alloy has tested to provide MOA accuracy for up to 20K rounds. They last longer and hold accuracy longer. Not sure if this has been independently verified, but that's what they report. The reason they claim this is their alloy isn't std 416R SS, it's something more wear resistant. Guns run cleaner -- something about the gas trap again trapping and/or allowing expelling of a bunch of the carbon that normally makes its way to the rear. The gas trap is placed right before the muzzle so I can somewhat imagine some carbon getting blown out the muzzle -- there's practically zero dwell, it's all based on the gas trap to provide enough back pressure, not too much unlike a Krink FH. AT isn't claiming piston upper clean, but they do claim they run cleaner than std carbines. Call me a bit skeptical on this one -- it would be interesting to see how many have made it through multiple-day carbine courses without choking. If they can digest thousands of rounds without choking, there's got to be some element of truth to the claim, I just have no way to characterize the extent of the claim. I just want to see more independnet testing, the pool of data is too limited. Maybe AT is now selling to civilians, they weren't when I called many months ago. But the fact is they've been in business for several years, they've got to be selling to someone who likes their stuff. Not sure if the bulk of their customer base is foreign military sales, LE or HSLD types. Anyone know? |
cbell never confirmed that his barrel was GT. He knew it was poly rifled, but that could have been an earlier generation barrel, before AT incorporated GT. Mach6 around the same time posted he chrono'd XM-193 at 2705 fps, this from a 9.5" GT barrel. POF OCC Link 9.25" vs 9.50": 2468/62 grain Green Tip vs 2705/XM-193. |
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